In the textile finishing sector, so-called mechanical compacting machines are known, comprising as their main components a feed roller, or “rough” roller, and a retarding roller or “rubberized” roller, which rotates at a lower speed than the feed roller. The fabric to be compacted is normally guided between the two rollers by a shaped blade element.
Compaction of the fabric is determined by the combined action of the shaped blade element that guides the fabric between the feed roller and the retarding roller, and the retarding roller which, rotating more slowly, “slows down” the fabric and therefore compacts it in the direction of feed.
In order to correctly compact the fabric along its entire transverse extension, the retarding roller must be positioned in close proximity and kept as parallel as possible to the feed roller.
Moreover, the retarding roller frequently detaches and then needs to be brought closer to the feed roller, for example, at each passing of a seam in correspondence with the gap between the rollers.
The movement of the retarding roller is generally effected by one or more pneumatic actuators which drive some levers, as described for example in documents U.S. Pat. No. 5,655,275 and U.S. Pat. No. 8,590,122.
Generally, the retarding roller is made to rest on the rough feed roller by applying high pressure to it, so as to reduce the times needed to move it closer. Consequently, the retarding roller knocks rather violently against the rough feed roller, which, due to the difference in the peripheral speed of the two rollers, tends to cause abrasion on the rubber of the retarding roller not covered by the fabric.
In order to work the fabric correctly, in fact, the retarding roller must be brought very close to the rough roller and perfectly parallel to it, but possibly not in contact, otherwise the rubber is worn out in a very short time.
In known solutions, after having rested the retarding roller on the feed roller and thereby obtaining the parallelism between the two, the pressure in the pneumatic actuators that move the levers on which the rubberized roller is mounted is drastically reduced, so that it remains just resting on the feed roller and, due to the thickness of the fabric passing between them, the two rollers are no longer in contact with each other.
One disadvantage of this solution is the short duration of the rubberized retarding roller which has to be replaced/ground frequently.
In fact, the abrasion effect indicated above occurs every time the retarding roller detaches from the fabric, and hence from the feed roller, then returns closer to it, that is, every time there is a seam.
Considering that a compacting machine can work at a speed generally comprised between 30 and 50 m/min, and that in the fabric there is a seam in correspondence with each end of the piece, that is about every 50 m, it is possible to estimate the number of “jumps” that the retarding roller performs in a working day of about 12 hours.
At a minimum speed of 30 m/min, about 21,600 m of fabric per day will be processed, for a total of approximately 432 seams.
This means that for 432 times a day the retarding roller detaches from the fabric and from the feed roller, and then is thrust back against it with high pressure, as explained above. Although high pressure is applied only for a fraction of a second, however, it is sufficient to cause abrasion of the retarding roller at the points of contact with the feed roller.
It is therefore evident that in a compacting machine of this type, it is necessary to grind and/or replace the retarding roller very frequently, about every two months, with consequent economic losses deriving from machine downtimes needed to carry out maintenance.
To solve this problem, compacting machines have been produced, provided with a spacer device which prevents the retarding roller from contacting the feed roller during the closing step. The known spacer device comprises idle rings installed at the opposite ends of the shaft of the feed roller. The rings have a slightly larger diameter than the diameter of the feed roller. In this way, when the retarding roller is thrust against the feed roller, there is a contact between the rings and the retarding roller, so that the retarding roller remains distanced from the feed roller and is free to rotate at a different speed without sliding against the rough surface of the feed roller.
One disadvantage of this known solution, however, is the fact that, to modify the distance between the retarding roller and the feed roller, for example depending on the thickness of the fabric to be treated, complicated operations are required to disassemble and reassemble the rings, which require the machine to be stopped in order to access the rings and replace them with others of different diameter. Also, changing the positioning distance between the rollers can in no way be automated.
One purpose of the present invention is to obtain a compacting machine provided with a positioning device for the rollers which overcomes at least one of the disadvantages of the state of the art.
In particular, the purpose of the invention is to reduce the problems associated with repeated sliding of the rubberized retarding roller with respect to the rough feed roller, and hence the consequent premature wear of the rubberized roller.
Another purpose is to obtain a positioning device that is highly reliable and which allows to repeat the correct positioning of the retarding roller with respect to the feed roller without them ever being in contact.
Another purpose of the present invention is to obtain a positioning device that can be regulated automatically and that allows for easy and rapid change of the reciprocal distance between the rollers.
One purpose of the present invention is also to provide a positioning device that is versatile and whose drive can be programmed according to the thickness, or type of fabric to be treated, and the degree of compaction required.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.